Merging C–H Vinylation with Switchable 6π-Electrocyclizations for Divergent Heterocycle Synthesis

Pyridinium-containing
polyheterocycles exhibit distinctive biological
properties and interesting electrochemical and optical properties
and thus are widely used as drugs, functional materials, and photocatalysts.
Here, we describe a unified two-step strategy by merging Rh-catalyzed
C–H vinylation with two switchable electrocyclizations, including
aza-6π-electrocyclization and all-carbon-6π-electrocyclization,
for rapid and divergent access to dihydropyridoisoquinoliniums and
dihydrobenzoquinolines. Through computation, the high selectivity
of aza-electrocyclization in the presence of an appropriate “HCl”
source under either thermal conditions or photochemical conditions
is shown to result from the favorable kinetics and symmetries of frontier
orbitals. We further demonstrated the value of this protocol by the
synthesis of several complex pyridinium-containing polyheterocycles,
including the two alkaloids berberine and chelerythrine.